For the perception of complex environmental sounds, the normal mammalian ear has an extremely wide dynamic range and high frequency selectivity. These auditory capabilities are achieved by cochlear high sensitivity, nonlinearity and sharp tuning. A cochlear amplifier has been proposed to amplify the basilarmembrane vibration evoked by low level sound and enhance mechanical frequency selectivity. A widely accepted speculation is that the amplifier works by obtaining energy from the outer hair cells (OHCs). Although isolated OHC electromotility in vitro has been intensively studied and the cochlear amplifier theory is generally accepted, the role of the OHC electromotility in the cochlear amplifier has not been tested in vivo and in sensitive cochleae. The long-term objective of the proposed work is to determine whether a cochlear amplifier feedback system utilizes OHC-generated energy. In order to achieve the long-term goal, it is essential to characterize the electrically evoked otoacoustic emissions (EEOAE). The EEOAE will be investigated in this initial study by focusing on the fine structure of the EEOAE. Our working hypothesis is that the ear canal-measured EEOAE is a vector summation of the multicomponents of the electrically evoked mechanical response in the cochlea. The fine structure of the EEOAE results from the cancellation and enhancement of the different components, and the fine structure indicates normal mechanical properties of a sensitive cochlea. To preserve cochlear sensitivity, an extracochlear electrical stimulation animal model will be used to generate the EEOAE. A method for detecting multicomponents of a single frequency signal will be implemented to analyze the EEOAE. The specific aims of the proposed study are to investigate i) how the fine structure of the EEOAE is generated; ii) what the relationship is between the EEOAE fine structure and cochlear sensitivity; and iii) what the correspondence is between the EEOAE and acoustically evoked cubic distortion product otoacoustic emission (DPOAE) fine structures. The responses of each of the components of the EEOAE to cochlear sensitivity changes and a simultaneously presented acoustic stimulus will be observed. Similarity of the multiple components between the EEOAE and the DPOAE will also be studied. Results from the proposed experiments will provide evidence that the fine structure results from the interaction of the multicomponents of the EEOAE, and that the multicomponent analysis method is a reliable method for quantification of the fine structure of the otoacoustic emissions.